1. Technical Field
The present invention relates to a catalyst suitable for the production of polyester, use of said catalyst, and a method of production using the catalyst.
2. Description of the Related Art
The production of polyesters generally takes place by means of reacting a diol with a dicarboxylic acid or a low dicarboxylic acid ester, for example, a dimethyl ester, to form the corresponding dicarboxylic acid ester, which is polycondensed at rising temperatures and reduced pressure in a single stage or in multiple stages. Various catalysts are used for the esterification and/or the transesterification and polycondensation, depending on the selection of the diols or the dicarboxylic acids or dicarboxylic acid esters.
Generally in this process, a catalyst is used that comprises the polyvalent metal cations, which are able to form transition complexes with the functional groups, particularly with the hydroxyl terminal groups, whereby preferred metal ions for the polycondensation have three or more free valencies. Typical examples are Sb3+, Pb4+, Ti4+, Bi3+, As3+, Si4+, Sn4+, Al3+, and Ge4+. In industrial practice, particularly for the polycondensation of polyethylene terephthalate (PET), Sb3+ and Ge4+ have proven satisfactory, whereby metal concentrations of 150 to 300 ppm Sb and 20 to 120 ppm Ge, depending on the type of polycondensation reactor, are effective.
Polyester products with a multiplicity of characteristics can be produced with the two metal ions mentioned above. Particularly with respect to the catalytically active component Sb3+, however, it is detrimental that this can possibly exercise harmful influences on the environment. There has therefore been no lack of attempts to establish other metal ions as catalytically effective components, particularly ones based on Ti.
EP 1 031 590 A2 discloses a catalyst for the preparation of polyesters, as well as the production and use of this catalyst. This catalyst comprises a fine-grained and porous substrate substance, as well as a catalytically effective metal compound adsorbed in the pores of this substrate substance.
WO 02/090419 discloses a composition and a method for the production of polyester. This composition comprises a substrate substance, on which catalytically effective metal compounds are adsorbed, as well as a phosphorus-containing component.
DE 103 39 742 A1 describes a catalyst, suitable for the production of polyesters, whereby the catalyst consists of a nanoscalic inorganic oxide as the substrate material, with at least one titanium-containing compound absorbed therein.
Detrimental with regard to the use of Ti as a catalytically active metal component in catalysts for polycondensation of polyesters, however, is the high level of sensitivity to hydrolysis, for example, of the customary titanium alkoxides and the tendency towards precipitation that is inherent in compounds of this type, as well as the ability of producing colored complex compounds, which have a detrimental effect on product quality. Furthermore, catalytically effective compositions based on titanium are not able to show sufficiently high activity in the solid state during polycondensation in the manufacture of polyester, whereby this is a process step that is particularly necessary for the production of polyester materials for packaging purposes.